Ah, what's old is new again.
Dark mode is all the rage on smartphones these days and it makes perfect sense that dramatically reducing all those battery-sucking bright whites to zero-energy blacks makes your device last longer between charges. It's also easier on the eyeballs and less noticeable in darker venues. I've turned on several dark mode themes in apps on my Google Pixel 2, but Android Q, due out in 2019, looks to deliver that system-wide, as per the article below. Can't wait (but I guess I have to, duh).
And the image below? That's a 1980s-vintage IBM 3270 terminal, which always had a black (i.e. Dark Mode) background. Full circle, once again.